1. Field of the Invention
This invention relates to a group of compounds classified in the field of organic chemistry as 4-[4-(substituted-amino)phenyl]- or heteroaryl-2,6-bis(heteroaryl)pyridines useful as color formers in pressure-sensitive carbonless duplicating systems and thermal marking systems, to a process for the preparation thereof and to pressure-sensitive carbonless duplicating systems and thermal marking systems containing the same.
2. Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as color formers for carbonless duplicating systems. Among the more important classes are the phenothiazines, for example N-benzoyl leuco methylene blue; fluorans, for example 2'-anilino-6'-diethylaminofluoran; phthalides, for example crystal violet lactone; arylsulfinate salts of Michler's Hydrol; substituted phenylpyridines and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457, 3,041,289 and 4,000,087, which issued July 5, 1955, July 23, 1957, June 26, 1962 and Dec. 28, 1976, respectively. Many of the color formers in the prior art suffer one or more disadvantages such as low tinctorial strength, poor light stability, poor xerographic copiability and low solubility in common organic solvents, the latter disadvantage thus requiring the use of specialized and expensive solvents in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copy systems.
The following appear to constitute the most pertinent prior art relative to the present invention.
Baumann et al., U.S. Pat. No. 3,985,376, patented Oct. 12, 1976 discloses compounds of the formula ##STR1## in which R.sup.1 and R.sup.2 are hydrogen or alkyl or aryl of one to eight carbon atoms which may bear alkoxy or halogen as a substituent;
R.sup.3 is hydrogen or alkyl of one to five carbon atoms; PA1 R.sup.4 is alkyl, haloalkyl, cyanalkyl, aryl or aralkyl of one to eight carbon atoms which may bear alkoxy as a substituent; PA1 R.sup.5 and R.sup.6 are hydrogen or carbalkoxy of two to five carbon atoms and R.sup.3 and R.sup.4 may be closed to form a ring. Specific compounds disclosed are those wherein R.sup.1 and R.sup.2 are each phenyl, R.sup.5 and R.sup.6 are each hydrogen, R.sup.3 is methyl and R.sup.4 is methyl, phenyl or p-ethoxyphenyl, and also those wherein R.sup.1 and R.sup.2 are each p-methoxyphenyl, R.sup.5 and R.sup.6 are each hydrogen and R.sup.3 and R.sup.4 are each methyl. The compounds are stated to be useful as dye precursors for pressure-sensitive recording material. PA1 R.sub.3 is hydrogen, lower-alkyl groups or lower-alkoxy groups; PA1 R.sub.4 and R.sub.5 are independently lower-alkyl groups, benzyl group or phenyl group, said lower-alkyl groups possibly being substituted with a cyano group, a chlorine atom or a lower-alkoxy group. The compounds are stated to produce a yellow color on heating in the presence of an electron acceptor. PA1 R.sub.2 is hydrogen, phenyl or non-tertiary lower-alkyl; PA1 R.sub.3 is hydrogen, non-tertiary lower-alkyl or non-tertiary lower-alkoxy; PA1 X is O or S; PA1 Z is 9-julolidinyl or a substituent having the formula ##STR6## in which: R.sub.4 is hydrogen, lower-alkyl, halo, lower-alkoxy, lower-alkoxycarbonyl or di-lower-alkylamino; PA1 R.sub.5 is lower-alkyl, and PA1 R.sub.6 is lower-alkyl, benzyl, cyano-lower-alkyl, or PA1 NR.sub.5 R.sub.6 is pyrrolidinyl, piperidinyl, morpholinyl or isoindolinyl.
M. Weiss, J. Amer. Chem. Soc. 74, 200-202 (1952) discloses in most pertinent part compounds of the formula ##STR2## wherein R is hydrogen and R' is phenyl, 4-methoxyphenyl, 3,4-methylenedioxyphenyl, 4-dimethylaminophenyl or 2-methoxyphenyl. These compounds were isolated as reaction products in a study of the Chichibabin synthesis.
E. Koenigs and E. Ruppelt, Ann. 509, 142-158 (1934) disclose as basic dyestuffs a number of 4-[p-dialkylaminophenyl]-pyridines.